Hello Jon,
Repeatedly re-creating an EntityManagerFactory would require more cpu cycles then having a single EntityManagerFactory. In TopLink an EntityManagerFactory is currently a wrapper around a singleton but this is not maindated by the specification and each Persistence Provider will implement this differently. I would recommend that you close the old EntityManagerFactory on undeploy as you may be left with artifacts (like mappings) from the original deployment.
--Gordon
-----Original Message-----
From: Jon Miller [mailto:jemiller_at_uchicago.edu]
Sent: Sunday, January 14, 2007 3:26 AM
To: Glassfish Persistence List
Subject: Is this pattern safe to use in a web app?
Hi all,
NetBeans 5.5 has a menu item labelled "Use EntityManager" which generates
code like the following. What I'm wondering is if you had several classes
that had the EntityManagerFactory stored in a private static field like
that, if it would wasting a lot of resources? Or, is it basically a
singleton for a given persistence unit behind the scenes anyway? Also, I
know at least for Hibernate when you create a SessionFactory, it's slow
because it has to parse the config files and what not. Is the same thing
true for TopLink? i.e. is it slow everytime you create a
EntityManagerFactory, or, only the first time? Also, if I don't close the
EntityManagerFactory when a web app is hot redeployed, would that cause a
memory leak? Tomcat seems to leak memory like a sive in general on webapp
redeploys, but, I don't want to exacerbate things. I should say that at the
moment, I'm just using Tomcat in standalone mode and not using an app
server.
Jon
package toplinktest;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class Test {
private static EntityManagerFactory emf =
Persistence.createEntityManagerFactory("ToplinkTestPU");
public Test() {
}
public void test() {
}
public void persist(Object object) {
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
try {
// TODO:
// em.persist(object); em.getTransaction().commit();
} catch (Exception e) {
e.printStackTrace();
em.getTransaction().rollback();
} finally {
em.close();
}
}
}